MediaWiki is the software that powers Wikipedia, its sister projects and thousands of wikis all over the world. It runs on most operating systems, is written in PHP, primarily uses the MySQL database server and uses jQuery as the client Javascript library. Development of MediaWiki is primarily supported by the Wikimedia Foundation, though volunteer community developers play a huge part as well.

This page should help you get started on the path to becoming a contributor to MediaWiki. It is not a tutorial; it just points you to various places where you can go learn whatever is necessary.

First of all, get Developer access and Gerrit tutorial done to download our code, test it and start submitting patches. There are two ways to set up your development environment: using a pre-configured virtual machine setup (vagrant), or manual.0

It's not necessary to download Wikipedia database dumps in order to develop MediaWiki features. In fact, in many cases it's easier to use a near-empty database with a few specially-crafted test pages. However, if for some reason you want to have a copy of Wikipedia, you can get a dump.

Following the Commit message guidelines, especially the Example section at the bottom, will automatically add a notification about your patch to the corresponding report in Phabricator. Hence there is no need anymore to add a "Please review" comment in the report.

You are expected to do some basic research yourself first: Look at the code, try to get some understanding what it is supposed to do, and try to find the probable place(s) where you need to make changes in order to fix the bug.

If you have a specific question about the bug itself, comment in the corresponding Phabricator report. "What do I have to do to fix this bug?" is not a good question to start with: The more specific your questions are, the more likely somebody can answer them quickly. If you have no idea at all how to fix the bug, maybe that bug is not (yet) for you - please consider finding an easier one first.

When asking, elaborate what you have tried and found out already, so others can help at the right level. Try to be specific - for example, copy and paste your commands and their output (if not too long) instead of paraphrasing in your own words. This avoids misunderstandings.

Please be patient when seeking input and comments. On IRC, don't ask to ask, just ask: most questions can be answered by other community members too if you ask on an IRC channel. If nobody answers, please ask on the bug report or wiki page related to the problem; don't just drop the question.

You do not need to be set as the assignee in a bug report or announce your plans before you start working on a bug, but it is welcome. At the latest when you are close to creating a patch for the bug, it is good to announce in a comment that you are working on it. Your announcement also helps others to not work on the bug at the same time and duplicate work.

Also note that if a bug report already has a recent link to a patch in Gerrit and is in the status PATCH_TO_REVIEW, you should choose a different bug to work on instead - avoid duplicating work. If the patch in Gerrit has not been merged and has not seen any changes for a long time, you could also pick up that existing patch and try to improve it.

If you stop working on a task you should remove yourself as the assignee of a bug report and reset the assignee to the default assignee, so others know that they can work on the bug report and don't expect you to still work on it.

By communicating early you will get more attention, feedback and help from community members.

Writing an extension for deployment — If you intend to have your extension deployed on Wikimedia sites (including possibly Wikipedia), additional scrutiny is warranted in terms of performance and security.

The following sections describe a few example areas in which you can contribute, but you are not limited to these areas!

In the upper right corner of a bug report you can see the product and component that the problem is located in. This provides you a hint about the Git repository that the code is located in, and about the development team which you could contact if you want to discuss it in a "broader" way (as comments in bug reports should preferably refer to the specific problem described in the report only).

System messages in MediaWiki or its extensions often need small corrections to the English text, but the source text can only be changed in the code by developers, contrary to translations. This has grown into a large backlog of usually very easy fixes (which might be as easy as fixing a typo).

Also, many messages are unclear and require better documentation (see Localisation#Message documentation). Missing documentation can also be added by just editing the /qqq subpage of the message on translatewiki.net, like all translations, but may require some study of the code to understand what a message is for: it's therefore optimal to start understanding the code, and very useful for the translators (who do not have such skills).

MediaWiki currently uses MySQL (and compatible ones) as the primary database back-end. It also supports other DBMSes, such as PostgreSQL and SQLite. However, almost all developers use MySQL and don't test other DBs, which consequently break on a regular basis. You're therefore advised to use MySQL when testing patches, unless you're specifically trying to improve support for another DB. In the latter case, make sure you're careful not to break MySQL (or write queries that are horribly inefficient in it), since MySQL is what everybody else uses.

JavaScript and CSS have become omnipresent in front-end code. You don't have to be familiar with JavaScript, jQuery and CSS to work on MediaWiki, but you might need to, depending on what you choose to work on.